The present invention relates to a fluorescent conversion filter that converts the light in the region between near-ultraviolet and blue to green light and an organic light emitting element including such a fluorescent conversion filter. The fluorescent conversion filter and the organic light emitting element are used preferably in display devices for civil or industrial use such as a light-emitting-type multicolor display, a light-emitting-type full-color display, a display panel and a back light.
Research and development of various light emitting elements have been vigorously explored to meet the increasing demands for flat panel displays for replacing conventional Brownian tubes. The electroluminescent element (hereinafter simply referred to as a xe2x80x9clight emitting elementxe2x80x9d) is an all-solid-state self-light-emitting element that meets the above described demands. The electroluminescent element has attracted much attention due to its very high resolution and very high visibility, which other display devices do not exhibit.
To provide a flat panel display with a multicolor display function or a full-color display function, light emitters of the three primary colors, i.e. red-light emitters, blue-light emitters and green-light emitters, are separately arranged in a matrix and the light emitters are controlled to emit light in the respective colors (cf. Japanese Unexamined Laid Open Patent Applications No. S57-157487, No. S58-147989 and No. H03-214593). It is technically difficult and expensive to use an organic light emitting element for a color display, since three kinds of light emitting materials for the three primary colors must be arranged very finely in a matrix. In addition, since the lives of the three different light emitting materials are not identical, chromaticity deviations are caused with elapse of time.
The three primary colors are obtained by transmitting the white light from a back light through color filters (cf. Japanese Unexamined Laid Open Patent Applications No.
H01-315988, No. H02-273496 and No. H03-194895). White light with high luminance is necessary to obtain the three primary colors at high luminance. However, any long-life organic light emitting element that emits white light at high luminance has not been obtained so far.
Japanese Unexamined Laid Open Patent Application No. H03-152897 discloses a planar and separate arrangement of fluorescent converter materials, which absorb the light from a light emitter and emit polychromatic fluorescent light. The planar and separate arrangement of fluorescent converter materials for emitting polychromatic fluorescent light is applied to the CRT""s and the plasma displays.
Japanese Unexamined Laid Open Patent Applications No. H03-152897 and H05-258860 disclose a color conversion method that uses fluorescent converter materials, which absorb the light from an organic light emitting element and emit fluorescent light in the visible wavelength region. Since the color of the light that the organic light emitting element emits is not limited to white, an organic light emitting element that emits light at higher luminance may be used as a light source. Japanese Unexamined Laid Open Patent Applications No. H03-152897, No. H08-286033 and No.H09-208944 disclose a color conversion method that uses an organic blue-light emitting element as a light source and converts the blue light to green light and red light by respective fluorescent dyes. By finely patterning the fluorescent conversion films, each including one of those fluorescent dyes, a full-color light-emitting type display may be constructed even when a weak energy ray such as a near ultraviolet ray and a visible ray from a light emitter is used.
The fluorescent conversion filter is patterned, in the similar manner as the inorganic fluorescent converter, by dispersing a fluorescent dye into liquid photoresist (photo-reactive polymer), forming a film of the dispersion liquid by spin coating and by patterning the formed film by the photolithographic technique (cf. Japanese Unexamined Laid Open Patent Applications No. H05-198921 and No. H05-258860). The fluorescent conversion filter is patterned also by dispersing a fluorescent dye or a fluorescent pigment into a basic binder and by etching the basic binder film with acidic aqueous solution (cf. Japanese Unexamined Laid Open Patent Application No. H09-208944).
The conventional light emitting display, based on the color conversion method that uses an organic blue-light-emitting element, fails to always obtain green light with a high color purity, since more than 10% of the light from the blue-light-emitting element is transmitted through the color conversion filter. In addition, the color purity is also impaired since fluorescent dye contained in the color filter emits light with the wavelength region of 550 nm and longer.
To obtain green light with a high color purity, a green color filter is laminated on the light emitting side of the fluorescent conversion filter. However, the green color filter impairs the color conversion efficiency, since the green color filter absorbs the light in the wavelength region between 500 and 550 nm.
In view of the foregoing, it is an object of the invention to provide a fluorescent conversion filter that converts the light in the region between near-ultraviolet and blue to green light and emits the green light with a high color purity. It is another object of the invention to provide an organic light emitting element including such a fluorescent conversion filter.
According to an aspect of the invention, there is provided a fluorescent conversion filter including: a fluorescent converter material selected from the group consisting of a fluorescent dye, a fluorescent pigment, and a mixture of a fluorescent dye and a fluorescent pigment; a light absorbing dye; and a matrix resin; the fluorescent converter material absorbing the light from a light emitter, the light being in a wavelength region between near-ultraviolet and blue; the fluorescent converter material emitting green light; the fluorescent converter material having an absorption band in a wavelength region between 450 and 500 nm; the fluorescent converter material being contained in the fluorescent conversion filter at a mixing ratio, at that the light absorbance of the fluorescent conversion filter is one or more in the wavelength region between 450 and 500 nm; the light absorbing dye having an absorption band in a wavelength region of 550 nm or longer; the light absorbing dye being contained in the fluorescent conversion filter at a mixing ratio, at that the light absorbance of the fluorescent conversion filter is 0.1 or more in a wavelength region between 550 and 650 nm.
According to an aspect of the invention, there is provided a fluorescent conversion filter including: a fluorescent conversion film; and a light absorption film laminated on the fluorescent conversion film; the fluorescent conversion film including a matrix resin and a fluorescent converter material selected from the group consisting of a fluorescent dye, a fluorescent pigment and a mixture of a fluorescent dye and a fluorescent pigment; the fluorescent converter material absorbing the light from a light emitter, the light being in a wavelength region between near-ultraviolet and blue; the fluorescent converter material emitting green light; the fluorescent converter material having an absorption band in a wavelength region between 450 and 500 nm; the fluorescent converter material being contained in the fluorescent conversion film at a mixing ratio, at that the light absorbance of the fluorescent conversion filter is 1 or more in the wavelength region between 450 and 500 nm; the light absorption film including a light absorbing dye and the matrix resin; the light absorbing dye having an absorption band in a wavelength region of 550 nm or longer; the light absorbing dye being contained in the light absorption film at a mixing ratio, at that the light absorbance of the fluorescent conversion filter is 0.1 or more in a wavelength region between 550 and 650 nm.
Advantageously, the light absorbing dye is an oxazine dye described in FIG. 4 by a general formula (I), where R1 is a hydrogen atom, an alkyl group, an aryl group or a heterocyclic group; R2 is a hydrogen atom, an alkyl group, an aryl group or a heterocyclic group; R3 is a hydrogen atom, an alkyl group, an aryl group or a heterocyclic group; R4 is a hydrogen atom, an alkyl group, an aryl group or a heterocyclic group; R1, R2, R3 and R4 are same with or different from each other; R5 is a hydrogen atom or a benzene ring; R6 is a hydrogen atom or a benzene ring; and X is an anion selected from the group consisting of Ixe2x88x92, Brxe2x88x92, ClO4xe2x88x92, BF4xe2x88x92, PF4xe2x88x92, and SbF4xe2x88x92.
Advantageously, the light absorbing dye is a cyanine dye described in FIG. 5 by a general formula (II), where R1 is a hydrogen atom, an alkyl group, an aryl group or a heterocyclic group; R2 is a hydrogen atom, an alkyl group, an aryl group or a heterocyclic group; R3 is a hydrogen atom, an alkyl group, an aryl group or a heterocyclic group; R4 is a hydrogen atom, an alkyl group, an aryl group or a heterocyclic group; R5 is a hydrogen atom, an alkyl group, an aryl group or a heterocyclic group; R6 is a hydrogen atom, an alkyl group, an aryl group or a heterocyclic group; R1, R2, R3, R4, R5 and R6 are same with or different from each other; and Xxe2x88x92 is an anion selected from the group consisting of Ixe2x88x92, Brxe2x88x92, ClO4xe2x88x92, BF4xe2x88x92, PF4xe2x88x92, SbF4xe2x88x92, and 1/2(SO42xe2x88x92).
Advantageously, the light absorbing dye is a cyanine dye described in FIG. 6 by a general formula (III), where R1 is a hydrogen atom, an alkyl group, an aryl group or a heterocyclic group; R2 is a hydrogen atom, an alkyl group, an aryl group or a heterocyclic group; R1, and R2 are same with or different from each other; and Xxe2x88x92 is an anion selected from the group consisting of Ixe2x88x92, Brxe2x88x92, ClO4xe2x88x92, BF4xe2x88x92, PF4xe2x88x92, SbF4xe2x88x92, and 1/2(SO42xe2x88x92).
Advantageously, the matrix resin is a photo-curing resin.
Advantageously, the matrix resin is a photo- and thermo-setting resin.
According to still another aspect of the invention, there is provided an organic light emitting element including any of the fluorescent conversion filters described above and an organic light emitter that emits light in a wavelength region between 450 and 520 nm.
Since the fluorescent converter material, having an absorption band in the wavelength region between 450 and 500 nm, is contained in the fluorescent conversion filter or in the fluorescent conversion film at a mixing ratio, at that the light absorbance of the fluorescent conversion filter is 1 or more in the wavelength region between 450 and 500 nm, the light from the light emitter is prevented from leakage in the wavelength region between 450 and 500 nm.
Since the light absorbing dye, having an absorption band in the wavelength region of more than 550 nm, is contained in the fluorescent conversion filter or in the light absorption film at a mixing ratio, at that the light absorbance of the fluorescent conversion filter is 0.1 or more in the wavelength region between 550 and 650 nm, the light with a wavelength of 550 nm or longer is interrupted.
The fluorescent conversion filter according to the invention, that emits and transmits light in the wavelength region between 500 and 550 nm selectively, facilitates outputting green light with a high color purity. The mono-layered fluorescent conversion filter including a layer that contains a fluorescent converter material and a light absorbing dye, facilitates simplifying the manufacturing process, since it is not necessary to dispose an individual light absorption film.
The photo-curing resin or the photo- and thermo-setting resin used for a matrix resin facilitates very fine patterning by the conventional photolithographic techniques.
The organic light emitting element according to the invention, that outputs the light from the organic light emitter through the fluorescent conversion filter described above, efficiently emits green light with a high color purity.